class ActiveSupport::MessageEncryptor

def decrypt(encrypted_message)
  cipher = new_cipher
  encrypted_data, iv, auth_tag = extract_parts(encrypted_message)
  # Currently the OpenSSL bindings do not raise an error if auth_tag is
  # truncated, which would allow an attacker to easily forge it. See
  # https://github.com/ruby/openssl/issues/63
  if aead_mode? && auth_tag.bytesize != AUTH_TAG_LENGTH
    throw :invalid_message_format, "truncated auth_tag"
  end
  cipher.decrypt
  cipher.key = @secret
  cipher.iv  = iv
  if aead_mode?
    cipher.auth_tag = auth_tag
    cipher.auth_data = ""
  end
  decrypted_data = cipher.update(encrypted_data)
  decrypted_data << cipher.final
rescue OpenSSLCipherError => error
  throw :invalid_message_format, error
end